88 
PROFESSOR W. RAMSAY AND DR. S. YOUNG 
These results are graphically shown on Plate 7. The curves were smoothed by 
constructing others showing the relations between temperature and pressure at equal 
vapour-densities, and then transferring back to the original sheet of curve paper. It 
can be judged by the position of the circles how nearly the observations agree with 
the smoothed curves. 
IV. Heats of Vaporisation .—From the thermodynamic equation 
L dp t 
s i —s 2 dt I 5 
the heats of vaporisation at definite intervals of temperature were calculated. The 
values of the expression dp/dt were calculated in the following manner. By means of 
the formula logy> = a+5of-j-c/T, the vapour-pressures at one-tenth of a degree above 
and below the definite temperature were calculated, and the difference was multiplied 
by 5 to obtain the values for 1°. This method gives results probably as nearly correct 
as it is possible to obtain. The pressures were reduced to grammes per square centi¬ 
metre, and the value of J was taken as 42,500. 
Temperature. 
dp 
dt 
dp 
dt 
dp t 
dt J 
«! — So 
L 
C. 
o 
0 
Abs. 
273 
in mms. 
8*843 
in grammes. 
12*023 
0-07723 
1207-7 
93-27 
10 
283 
12-695 
17-26 
0-11493 
789-8 
90-77 
20 
293 
17-585 
23-91 
0-16483 
533-3 
87-90 
30 
303 
23-720 
32-25 
0-22992 
372-2 
85’60 
40 
313 
31-160 
42-37 
0-3] 200 
266-6 
83-18 
50 
323 
40-095 
54-51 
0-41430 
195-4 
80-95 
60 
333 
50-620 
68-82 
0-53924 
146-2 
78-84 
70 
343 
62-840 
85-44 
0-68932 
110-58 
76-42 
80 
353 
77-005 
104-70 
0-86958 
85-04 
73-95 
90 
363 
93-010 
123-46 
1-0801 
66-10 
71-39 
100 
373 
110-48 
150-21 
1-3183 
51-85 
68-35 
110 
383 
131-48 
178-76 
1-6113 
40-95 
65-98 
120 
393 
153-95 
209-3 
1-9355 
32-36 
62-63 
130 
403 
178-61 
242-8 
2-3027 
25-67 
59-11 
140 
413 
205-8 
279-8 
2-7191 
20-42 
55-52 
150 
423 
234-9 
319-4 
3-1786 
16-10 
51-18 
160 
433 
266-65 
362-5 
3-6936 
12-45 
45-99 
170 
443 
300-4 
408-4 
4-2572 
9-324 
39-69 
180 
453 
336-4 
457-4 
4-8751 
6-478 
31-58 
185 
458 
363-0 
493-5 
5-3186 
5-035 
26-78 
190 
463 
407-0 
553-4 
6-0282 
3-467 
20-90 
192 
465 
446-0 
606-4 
6-6344 
2-578 
17-10 
193 
466 
472-0 
641-7 
7-0364 
1-942 
13-67 
The heats of vaporisation have been determined by other observers; Brix 
(‘Liebig’s Annalen,’ vol. 44, 1842, p. 169) gives determinations of the heats of 
vaporisation of water, alcohol, and ether. Translating Reaumur into Centigrade 
degrees, that of water becomes 539‘6 calories; of alcohol, 214’25 calories; and of 
ether, 89‘96 calories. Determinations were next made by Andrews (‘ Chem. Soc. 
Journ.,’ vol. 1 , 1849, p. 27), who found 90’5 calories. The sample of ether he employed 
